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From: Michael Ellerman <mpe@ellerman.id.au>
To: Nathan Lynch <nathanl@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc: aik@ozlabs.ru, tyreld@linux.ibm.com, brking@linux.ibm.com,
	ajd@linux.ibm.com, aneesh.kumar@linux.ibm.com
Subject: Re: [PATCH 6/6] powerpc/rtas: constrain user region allocation to RMA
Date: Tue, 19 Jan 2021 20:00:43 +1100	[thread overview]
Message-ID: <87mtx5qp1g.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20210114220004.1138993-7-nathanl@linux.ibm.com>

Nathan Lynch <nathanl@linux.ibm.com> writes:
> Memory locations passed as arguments from the OS to RTAS usually need
> to be addressable in 32-bit mode and must reside in the Real Mode
> Area. On PAPR guests, the RMA starts at logical address 0 and is the
> first logical memory block reported in the LPAR’s device tree.
>
> On powerpc targets with RTAS, Linux makes available to user space a
> region of memory suitable for arguments to be passed to RTAS via
> sys_rtas(). This region (rtas_rmo_buf) is allocated via the memblock
> API during boot in order to ensure that it satisfies the requirements
> described above.
>
> With radix MMU, the upper limit supplied to the memblock allocation
> can exceed the bounds of the first logical memory block, since
> ppc64_rma_size is ULONG_MAX and RTAS_INSTANTIATE_MAX is 1GB.

Why does the size of the first memory block matter for radix?

The 1GB limit is sufficient to make it accessible by 32-bit code.

> (512MB is a common size of the first memory block according to a small sample of
> LPARs I have checked.)

That's the minimum we request, see prom_init.c:

	/* option vector 2: Open Firmware options supported */
	.vec2 = {
		.byte1 = OV2_REAL_MODE,
		.reserved = 0,
		.real_base = cpu_to_be32(0xffffffff),
		.real_size = cpu_to_be32(0xffffffff),
		.virt_base = cpu_to_be32(0xffffffff),
		.virt_size = cpu_to_be32(0xffffffff),
		.load_base = cpu_to_be32(0xffffffff),
		.min_rma = cpu_to_be32(512),		/* 512MB min RMA */

Since v4.12 in 2017.

cheers

  parent reply	other threads:[~2021-01-19  9:02 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14 21:59 [PATCH 0/6] powerpc/rtas: miscellaneous cleanups, user region allocation Nathan Lynch
2021-01-14 21:59 ` [PATCH 1/6] powerpc/rtas: improve ppc_rtas_rmo_buf_show documentation Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:50   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 2/6] powerpc/rtas-proc: remove unused RMO_READ_BUF_MAX Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 3/6] powerpc/rtas: remove ibm_suspend_me_token Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 4/6] powerpc/rtas: move syscall filter setup into separate function Nathan Lynch
2021-01-15  4:39   ` Alexey Kardashevskiy
2021-01-15 16:04     ` Nathan Lynch
2021-01-15  5:49   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 5/6] powerpc/rtas: rename RTAS_RMOBUF_MAX to RTAS_USER_REGION_SIZE Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:56     ` Nathan Lynch
2021-01-18  4:15       ` Alexey Kardashevskiy
2021-01-20  1:17         ` Nathan Lynch
2021-01-20  5:05           ` Alexey Kardashevskiy
2021-01-21 15:17             ` Nathan Lynch
2021-01-15  6:10   ` Andrew Donnellan
2021-01-15 12:04   ` kernel test robot
2021-01-14 22:00 ` [PATCH 6/6] powerpc/rtas: constrain user region allocation to RMA Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:38     ` Nathan Lynch
2021-01-18  4:12       ` Alexey Kardashevskiy
2021-01-20  0:39         ` Nathan Lynch
2021-01-20  4:49           ` Alexey Kardashevskiy
2021-01-20 12:06           ` Michael Ellerman
2021-01-21 15:27             ` Nathan Lynch
2021-01-23  1:54               ` Alexey Kardashevskiy
2021-01-19  9:00   ` Michael Ellerman [this message]
2021-01-19 21:00     ` Nathan Lynch
2021-01-20 12:13       ` Michael Ellerman
2021-01-21  0:26         ` Nathan Lynch

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